The present invention relates to a method of increasing thermal conductivity of a fuser member useful in fusing toner images in an electrostatographic reproducing, including digital, apparatus. The present invention further relates to a fuser member prepared by such a method, having increased thermal conductivity. More specifically, the present invention relates to methods for increasing thermal conductivity of a fuser member by orienting anisotropic fillers and optional other fillers such as fluorocarbon fillers or fluorocarbon liquids, in a manner which results in maximum heat transfer.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which may be the photosensitive member itself or other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes it to be firmly bonded to the support.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat may be applied by heating one or both of the rolls, plate members, or belt members.
It is important in the fusing process that minimal or no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser, and accordingly it is desired to provide a fusing surface which has a low surface energy to provide the necessary release.
To ensure and maintain good release properties of the fuser, it has become customary to apply release agents to the fuser roll during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils such as polydimethyl siloxane (PDMS), mercapto oils, amino oils, and other silicone oils to prevent toner offset. The fuser oils may contain functional groups or may be non-functional, or may be blends of functional and nonfunctional.
Fillers have been added to the outer layer of fuser members having elastomer layers in order to increase thermal conductivity thereof.
U.S. Pat. No. 5,464,698 discloses a fuser member having a layer including a cured fluorocarbon random copolymer having subunits of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene, and having tin oxide fillers in combination with alkali metal oxides and/or alkali metal hydroxide fillers incorporated into the fuser layer.
U.S. Pat. No. 5,292,606 discloses a fuser roll having a base cushion layer comprising a condensation-crosslinked polydimethylsiloxane elastomer and having zinc oxide particles dispersed therein.
U.S. Pat. No. 5,464,703 discloses a fuser member having a base cushion layer including a crosslinked poly(dimethylsiloxane-fluoroalkylsiloxane) elastomer having tin oxide particles dispersed therein.
U.S. Pat. No. 5,563,202 discloses a fuser member having a base cushion layer having a crosslinked poly(dimethylsiloxane-fluoroalkylsiloxane) elastomer having tin oxide particles dispersed therein.
U.S. Pat. No. 5,466,533 discloses a fuser member having an overlying layer comprising a crosslinked polydiphenylsiloxane-poly(dimethylsiloxane) elastomer having zinc oxide particles dispersed therein.
U.S. Pat. No. 5,474,852 discloses a fuser member having an overlying layer comprising a crosslinked polydiphenylsiloxane-poly(dimethylsiloxane) elastomer having tin oxide particles dispersed therein.
U.S. Pat. No. 5,480,724 discloses a fuser member having a base cushion layer comprising a condensation-crosslinked polydimethylsiloxane elastomer having tin oxide particles dispersed therein.
U.S. Pat. No. 5,547,759 discloses a fuser member having a release coating comprising an outermost layer of fluoropolymer resin bonded to a fluoroelastomer layer by means of a fluoropolymer-containing polyamide-imide primer layer. Also disclosed is use of zinc oxide.
U.S. Pat. No. 5,595,823 discloses a fuser member having a layer including a cured fluorocarbon random copolymer having subunits of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene and having aluminum oxide filler along with alkali metal oxides and/or alkali metal hydroxide fillers incorporated into the fuser member layer.
U.S. Pat. No. 5,587,245 discloses a fuser member having an outer layer of an addition crosslinked polyorganosiloxane elastomer and zinc oxide particles dispersed therein.
Fillers are added to outer fusing layers in order to increase the thermal conductivity so as to reduce the temperature needed to promote fusion of toner to paper and to save energy consumption. Efforts have been made to increase the thermal conductivity which will allow for increased speed of the fusing process by reducing the amount of time needed to sufficiently heat the fuser member to promote fusing. Efforts have also been made to increase toner release in order to prevent toner offset which may lead to inadequate copy quality, inferior marks on the copy, and toner contamination of other parts of the machine.
Therefore, it is desirable to provide a method for increasing the thermal conductivity of a fuser member. It is further desirable that such method also allows for production of a fuser member having a combination of outer layer and filler material which provides an increase in release and a decrease in the occurrence of toner offset. It is also desirable that such method allows for production of a fuser member having an outer layer which provides for an increase in the fusing speed at a set temperature, or in the alternative, allows for use of a reduced temperature at normal or standard fusing speeds. It is also desirable to that such method provides a fuser member having increased wear resistance, and increased fusing life.